Re: Function called twice

[Jordan Wilson via Digitalmars-d-learn]

On Friday, 2 August 2019 at 22:35:53 UTC, Adam D. Ruppe wrote:
On Friday, 2 August 2019 at 21:44:28 UTC, Jordan Wilson wrote:
        // outputs 1 2 2 3
        z.map!(a => tuple!("number","iseven")(a, a.isEven))
         .filter!(a => a.iseven)
         .array;

I *think* what's happening here is first it calls map() first 
going into the filter... then it gets called again when it is 
being evaluated for the array.

So like basically consider if you had:

if(filter(a())
   array ~= a();


that kind of thing. I think anyway, I'm not entirely sure but 
it fits what I can see happening here.

but idk why it is actually doing this in the phobos 
implementation

In my real-world case "isEven" is a long running function. I'll 
put an .array after the map and see if it makes a difference.

Thanks,

Jordan